Concave Ultrasound Transducers and 3D Arrays

ABSTRACT

A Multiple Aperture Ultrasound Imaging (MAUI) probe or transducer is uniquely capable of simultaneous imaging of a region of interest from separate apertures of ultrasound arrays. Some embodiments provide systems and methods for designing, building and using ultrasound probes having continuous arrays of ultrasound transducers which may have a substantially continuous concave curved shape in two or three dimensions (i.e. concave relative to an object to be imaged). Other embodiments herein provide systems and methods for designing, building and using ultrasound imaging probes having other unique configurations, such as adjustable probes and probes with variable configurations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. 119 of U.S.Provisional Patent Application No. 61/392,896, filed Oct. 13, 2010,titled “Multiple Aperture Medical Ultrasound Transducers,” whichapplication is incorporated herein by reference in its entirety.

This application is related to U.S. Pat. No. 8,007,439, titled “Methodand Apparatus to Produce Ultrasonic Images Using Multiple Apertures”,and PCT Application No. PCT/US2009/053096, filed Aug. 7, 2009, titled“Imaging with Multiple Aperture Medical Ultrasound and Synchronizationof Add-on Systems.” This application is also related to U.S. patentapplication Ser. No. 12/760,327 filed Apr. 14, 2010, titled “MultipleAperture Ultrasound Array Alignment Fixture”, and U.S. patentapplication Ser. No. 12/760,375, filed Apr. 14, 2010, titled “UniversalMultiple Aperture Medical Ultrasound Probe”, and U.S. patent applicationSer. No. 13/029,907, filed Feb. 17, 2011, titled “Point SourceTransmission and Speed-of-Sound Correction Using Multi-ApertureUltrasound Imaging”.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

The present invention relates generally to imaging techniques used inmedicine, and more particularly to medical ultrasound, and still moreparticularly to an apparatus for producing ultrasonic images usingmultiple apertures.

BACKGROUND

In conventional ultrasonic imaging, a focused beam of ultrasound energyis transmitted into body tissues to be examined and the returned echoesare detected and plotted to form an image. In echocardiography, the beamis usually stepped in increments of angle from a center probe position,and the echoes are plotted along lines representing the paths of thetransmitted beams. In abdominal ultrasonography, the beam is usuallystepped laterally, generating parallel beam paths, and the returnedechoes are plotted along parallel lines representing these paths.

The basic principles of conventional ultrasonic imaging are described inthe first chapter of Echocardiography, by Harvey Feigenbaum (LippincottWilliams & Wilkins, 5th ed., Philadelphia, 1993). It is well known thatthe average velocity v of ultrasound in human tissue is about 1540m/sec, the range in soft tissue being 1440 to 1670 m/sec (P. N. T.Wells, Biomedical Ultrasonics, Academic Press, London, New York, SanFrancisco, 1977). Therefore, the depth of an impedance discontinuitygenerating an echo can be estimated as the round-trip time for the echomultiplied by v/2, and the amplitude is plotted at that depth along aline representing the path of the beam. After this has been done for allechoes along all beam paths, an image is formed. The gaps between thescan lines are typically filled in by interpolation.

In order to insonify the body tissues, a beam formed by an array oftransducer elements is scanned over the tissues to be examined.Traditionally, the same transducer array is used to detect the returningechoes. The use of the same transducer array to both produce the beamand detect returning echoes is one of the most significant limitationsin the use of ultrasonic imaging for medical purposes; this limitationproduces poor lateral resolution. Theoretically, the lateral resolutioncould be improved by increasing the aperture of the ultrasonic probe,but the practical problems involved with aperture size increase havekept apertures small and lateral resolution diminished. Unquestionably,ultrasonic imaging has been very useful even with this limitation, butit could be more effective with better resolution.

In the practice of cardiology, for example, the limitation on singleaperture size is dictated by the space between the ribs (the intercostalspaces). For scanners intended for abdominal and other use, thelimitation on aperture size is a serious limitation as well. The problemis that it is difficult to keep the elements of a large aperture arrayin phase because the speed of ultrasound transmission varies with thetype of tissue between the probe and the area of interest. According toWells (Biomedical Ultrasonics, as cited above), the transmission speedvaries up to plus or minus 10% within the soft tissues. When theaperture is kept small, the intervening tissue is assumed to behomogeneous, and any variation is consequently ignored. When the size ofthe aperture is increased to improve the lateral resolution, theadditional elements of a phased array may be out of phase and mayactually degrade the image rather than improve it.

In the case of abdominal imaging, it has also been recognized thatincreasing the aperture size could improve the lateral resolution.Although avoiding the ribs is not a problem, beam forming using asparsely filled array and, particularly, tissue speed variation needs tobe compensated. With single aperture ultrasound probes, it has beencommonly assumed that the beam paths used by the elements of thetransducer array are close enough together to be considered similar intissue density profile, and therefore that no compensation wasnecessary. The use of this assumption, however, severely limits the sizeof the aperture that can be used.

The problems of limited total aperture size have been addressed by thedevelopment of multiple aperture ultrasound imaging techniques as shownand described for example in U.S. Pat. No. 8,007,439, and US PatentApplication Publication 2011/0201933.

SUMMARY OF THE DISCLOSURE

In one embodiment, an ultrasound imaging system is provided, comprisingan ultrasound transducer array, the ultrasound transducer array having aconcave curvature about at least one axis, a first transmit aperture inthe ultrasound transducer array configured to insonify a scatterer withultrasound energy, a first receive aperture in the ultrasound transducerarray configured to receive ultrasound echoes from the scatterer, thefirst receive aperture being located apart from the first transmitaperture, and a control system in electronic communication with theultrasound transducer array, the control system configured to accesscalibration data describing a position and orientation of the firsttransmit aperture and the first receive aperture, the control systemconfigured to form an ultrasound image with the echoes received by thefirst receive aperture.

In some embodiments, the system further comprises a second receiveaperture in the ultrasound transducer array configured to receive echoesfrom the scatterer, the second receive aperture being located apart fromthe first transmit aperture and the first receive aperture, wherein thecontrol system is configured to access calibration data describing aposition and orientation of the second receive aperture, and wherein thecontrol system is configured to form an ultrasound image with the echoesreceived by the first and second receive apertures.

In some embodiments, the ultrasound transducer array has a concavecurvature about at least two axes.

In one embodiment, the calibration data is stored in the control system.In other embodiments, the calibration data is stored remotely from thecontrol system. In one embodiment, the calibration data is stored in achip housed within a probe housing along with the array.

A method of ultrasound imaging is provided, comprising, transmittingultrasound energy towards a scatterer with transmit aperture on anultrasound transducer array having a concave curvature about at leastone axis, receiving ultrasound echoes from the scatterer with a firstreceive aperture on the ultrasound transducer array, obtainingcalibration data containing a position and orientation of ultrasoundtransducers in the first transmit aperture and the first receiveaperture, and forming an ultrasound image with the ultrasound echoesreceived by the first receive aperture.

In some embodiments, the method further comprises receiving ultrasoundechoes from the scatterer with a second receive aperture on theultrasound transducer array; obtaining calibration data containing aposition and orientation of ultrasound transducers in the second receiveaperture, and forming an ultrasound image with the ultrasound echoesreceived by the first and second receive apertures.

Another ultrasound imaging system comprises an ultrasound transducerarray; a first transmit aperture in the ultrasound transducer arrayconfigured to insonify a scatterer with ultrasound energy, a firstreceive aperture in the ultrasound transducer array configured toreceive ultrasound echoes from the scatterer, the first receive aperturebeing located apart from the first transmit aperture, a second receiveaperture in the ultrasound transducer array configured to receiveultrasound echoes from the scatterer, the second receive aperture beinglocated apart from the first transmit aperture and the first receiveaperture, and a control system in electronic communication with theultrasound transducer array, the control system configured to change atotal aperture size of the system by switching from receiving echoeswith the first receive aperture to receiving echoes with the secondreceive aperture.

In one embodiment, the control system is configured to accesscalibration data describing a position and orientation of the firsttransmit aperture, the first receive aperture, and the second receiveaperture, wherein the control system is configured to form an ultrasoundimage with the echoes received by the first and second receiveapertures.

In some embodiments, the control system is configured to change thetotal aperture size automatically upon detection of an obstruction.

An ultrasound imaging system is also provided, comprising an ultrasoundtransducer array, a first transmit aperture in the ultrasound transducerarray configured to insonify a scatterer with ultrasound energy; asecond transmit aperture in the ultrasound transducer array configuredto insonify the scatterer with ultrasound energy, a first receiveaperture in the ultrasound transducer array configured to receiveultrasound echoes from the scatterer, the first receive aperture beinglocated apart from the first transmit aperture; a second receiveaperture in the ultrasound transducer array configured to receiveultrasound echoes from the scatterer, the second receive aperture beinglocated apart from the first transmit aperture and the first receiveaperture, and a control system in electronic communication with theultrasound transducer array, the control system configured to change anaperture view angle of the system by switching from transmittingultrasound energy with the first transmit aperture to transmittingultrasound energy with the second transmit aperture, and switching fromreceiving echoes with the first receive aperture to receiving echoeswith the second receive aperture, wherein a transmit/receive anglebetween the first transmit aperture and the first receive aperture isapproximately the same as the transmit/receive angle between the secondtransmit aperture and the second receive aperture.

In one embodiment, the control system is configured to accesscalibration data describing a position and orientation of the firsttransmit aperture, the first receive aperture, and the second receiveaperture, wherein the control system is configured to form an ultrasoundimage with the echoes received by the first and second receiveapertures.

In another embodiment, the control system is configured to change theaperture view angle automatically upon detection of an obstruction.

A method of ultrasound imaging is provided, comprising transmittingultrasound energy towards a scatterer with a first transmit aperture onan ultrasound transducer array having a concave curvature about at leastone axis, receiving ultrasound echoes from the scatterer with a firstreceive aperture on the ultrasound transducer array, detecting anobstruction between the scatterer and the first receive aperture, andafter detecting the obstruction, receiving ultrasound echoes from thescatterer with a second receive aperture on the ultrasound transducerarray.

In some embodiments, the detecting step is performed by a sonographer.In other embodiments, the detecting step is performed automatically by acontrol system.

In one embodiment, the transducer array has a concave curvature about atleast two axes.

In one embodiment, the after detecting step further comprises afterdetecting the obstruction, receiving ultrasound echoes from thescatterer with the second receive aperture on the ultrasound transducerarray, wherein the obstruction is not located between the scatterer andthe second receive aperture.

A method of ultrasound imaging is provided, comprising transmittingultrasound energy towards a scatterer with a first transmit aperture onan ultrasound transducer array having a concave curvature about at leastone axis, receiving ultrasound echoes from the scatterer with a firstreceive aperture on the ultrasound transducer array; detecting anobstruction between the scatterer and the first transmit aperture, andafter detecting the obstruction, transmitting ultrasound energy towardsthe scatterer with a second transmit aperture on the ultrasoundtransducer array.

In one embodiment, the detecting step is performed by a sonographer. Inanother embodiment, the detecting step is performed automatically by acontrol system.

In some embodiments, the transducer array has a concave curvature aboutat least two axes.

Another embodiment of an ultrasound imaging device comprises a probehousing, at least two ultrasound transducer arrays disposed on our nearthe probe housing, and at least one hinge mechanism configured to coupleeach of the ultrasound transducer arrays to the probe housing, the hingemechanisms configured to allow adjustment of the position or orientationof the ultrasound transducer arrays so as to conform to a physiology ofinterest.

In some embodiments, the device further comprises a locking mechanismconfigured to lock the hinge mechanisms.

A method of ultrasound imaging is provided, comprising placing anultrasound imaging probe having at least two ultrasound arrays intocontact with a patient, allowing each of the ultrasound arrays toindividually conform to the physiology of the patient, locking theultrasound arrays into a conformed configuration, calibrating theultrasound imaging probe in the conformed configuration, and after thecalibrating step, generating ultrasound images of the patient with theultrasound imaging probe.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an illustration of an ultrasound system control panel withaperture view angle and aperture width controls.

FIG. 2 is a schematic diagram of a concave curvilinear transducer arraywhere various elements are designated as transmit and receive apertures.

FIG. 2A is a schematic diagram of a concave curvilinear transducer arraywhere elements are put to use in the reciprocal transmit or receivefunction relative to FIG. 2.

FIG. 2B is a schematic diagram of an embodiment of a concave curvilineartransducer array where elements of transmit and receive apertures arepredesignated to insonify each other in rapid succession using likesized apertures.

FIG. 2C is a schematic diagram of an embodiment of a concave curvilineartransducer array demonstrating how transmit and receive apertures can bewidened around a desired view angle to achieve greater resolution of thetarget area.

FIG. 3 is a schematic diagram of an embodiment of a concave curvilineartransducer array illustrating a pulse transmitted by a single designatedtransmit aperture and being received by multiple designated receiveapertures.

FIG. 3A is a schematic diagram of an embodiment of a concave curvilineartransducer array where the transmit aperture and multiple receiveapertures can be electronically controlled to operate in differentpositions.

FIG. 4 is a schematic diagram of an embodiment a concave curvilinearmatrix with curvature in two orthogonal directions, also referred to asa Three Dimensional (3D) array. Each element in a 3D array is displacedrelative to adjacent elements in all of x, y, and z axes. In thisillustration, an element or elements of a transmit aperture isdesignated to insonify the medium. Multiple targets in the medium areillustrated for the purpose of demonstrating how volumetric data may begathered. Multiple receive apertures are illustrated to demonstrated howsimultaneous gathering of data may involve timing and tissue speed ofsound adjustments.

FIG. 4A schematically illustrates an embodiment of a 3D array. Multipletransmit apertures T₁ through T_(N) are indicated for the purpose ofdemonstrating transmit pulses being received on one or more receiveapertures R₂ and/or R₃. A single target is indicated for the purpose ofdemonstrating how data may be gathered.

FIG. 4B schematically illustrates an embodiment of a 3D array being usedto collect data for a 2D longitudinal slice along the x axis. In thisinstance, a line of elements in the transverse axis z are being used toform transmit aperture T₁ Data along the longitudinal slice may becollected by elements located in receive aperture R₂. Multiple transmitapertures, identified as T₁ through T₅ that can be used along the lengthof the longitudinal slice to assist in data collection over time.Another receive aperture R₃ is indicated that can be used to collecteither simultaneous data for the same transverse slice, or separate datafor a different longitudinal slice.

FIG. 4C schematically illustrates an embodiment of a 3D array being usedto collect data for a 2D transverse slice along the z axis. In thisinstance, a line of elements in the longitudinal axis x are being usedto form transmit aperture T₁ Data along the transverse slice may becollected by elements located in receive aperture R₂. Multiple transmitapertures T₁ through T₅ are indicated that can be used along the lengthof the longitudinal slice to assist in data collection over time.Another receive aperture R₃ is indicated that can be used to collecteither simultaneous data for the same transverse slice, or separate datafor a different transverse slice.

FIG. 4D illustrates a data volume with a 2D longitudinal slice of datahighlighted within the volume. This illustrates a capability of multipleaperture imaging to interchange volumetric 3D/4D imaging with higherresolution 2D imaging in near real time to allow for simultaneouspresentation on a display.

FIG. 4E illustrates a data volume with a 2D transverse slice of datahighlighted within the volume. This illustrates a capability of multipleaperture imaging to interchange volumetric 3D/4D imaging with higherresolution 2D imaging in near real time to allow for simultaneouspresentation on a display.

FIG. 5 is a schematic view showing a concave curvilinear probe over amedium of tissue with a relatively large radius curvature (e.g. abdomen,pelvis, etc.).

FIG. 5A is a bottom view of an embodiment of a curvilinear array (e.g.,1D, 1.5D or 2D) in a probe such as that shown in FIG. 5.

FIG. 5B is a bottom view of an embodiment of a matrix array (e.g., 2D or3D) in a probe such as that shown in FIG. 5.

FIG. 5C is a bottom view of an embodiment of a CMUT array in a probesuch as that shown in FIG. 5.

FIG. 6 is a schematic view showing an embodiment of a concavecurvilinear probe over a medium of tissue with relatively small radiuscurvature (e.g. arm, leg, neck, wrist, ankle, etc.).

FIG. 6A is a schematic view of an embodiment of a concave curvilineararray similar to that of FIG. 6, but in a probe housing with flexconnections that allow for cable connections to be made on the side ofthe probe housing.

FIG. 6B is a bottom view of an embodiment of a curvilinear array (e.g.,1D, 1.5D or 2D) in a probe such as those shown in FIGS. 6 and 6A.

FIG. 6C is a bottom view of an embodiment of a curved matrix (e.g., 2Dor 3D) array in a probe such as those shown in FIGS. 6 and 6A.

FIG. 6D is a bottom view of an embodiment of a CMUT array in a probesuch as those shown in FIGS. 6 and 6A.

FIG. 7 is a plan view of a concave transducer housing of an embodimentof the probe of FIG. 6A with an adjustable handle aligned with thelongitudinal axis of the array.

FIG. 7A is a plan view of a concave transducer housing of an embodimentof the probe of FIG. 6A with an adjustable handle aligned with thetransverse axis of the array.

FIG. 7B is a side schematic view showing a concave curvilinear probe ofFIG. 7A over a medium of tissue with a relatively large-radius curvature(e.g. abdomen, pelvis, etc.).

FIG. 7C is a bottom view of a curvilinear array (e.g., 1D, 1.5D or 2D)available for use with the probe styles illustrated in FIGS. 7A-7B.

FIG. 7D is a bottom view of a matrix array (e.g., 2D or 3D) availablefor use with the probe styles illustrated in FIGS. 7A-7B.

FIG. 7E is a bottom view of a CMUT array available for use with theprobe style illustrated in FIGS. 7A-7B.

FIG. 7F is a bottom view of a concave curved transducer array (e.g., 3Dor CMUT) arranged in an elliptical pattern, as used in a probe such asthat shown in FIGS. 7A-7B.

FIG. 7G is a plan view of a concave array probe housing identifying thesection line for FIG. 7H.

FIG. 7H is a sectional view of the concave array probe housing of FIG.7G taken along line A-B. This embodiment illustrates flex connectors andcabling connections on the right side or bottom of the probe. Acalibration chip, synchronization module, probe position displacementsensor are also shown in the probe handle.

FIG. 8 is a diagram showing an embodiment of an adjustable ultrasoundprobe. This version of an adjustable probe has five arrays, each havingan associated flex connector. A calibration chip, synchronizationmodule, probe position displacement sensor are also shown in the probehandle.

FIG. 8A is a diagram showing the five arrays of the probe of FIG. 8deployed in a custom contoured arrangement to match the desiredphysiology.

FIG. 8B is a side view of two of the arrays of the probe of FIG. 8,showing details of an embodiment of adjustable hinges between the arraysand a tension cable. The adjustable hinges are shown connected to thebacking block of each array.

FIG. 8C is a bottom view illustrating an embodiment of the individualarrays (e.g., 1D or 1.5D) in a probe such as that shown in FIG. 8.

FIG. 8D is a bottom view illustrating an embodiment of the individualarrays as matrix arrays (e.g., 2D) in a probe such as that shown in FIG.8.

FIG. 8E is a bottom view illustrating an embodiment of the individualarrays as CMUT arrays in a probe such as that shown in FIG. 8.

DETAILED DESCRIPTION

Some embodiments herein provide systems and methods for designing,building and using ultrasound probes having continuous arrays ofultrasound transducers which may have a substantially continuous concavecurved shape in two or three dimensions (i.e. concave relative to anobject to be imaged). Other embodiments herein provide systems andmethods for designing, building and using ultrasound imaging probeshaving other unique configurations, such as adjustable probes and probeswith variable configurations.

The use of calibrated multiple aperture array or arrays combined withmultiple aperture imaging methods allow for custom shaped, concave oreven adjustable probes to be utilized in ultrasound imaging. Further,uniquely shaped ultrasound probe solutions are desirable in order toovercome the various shortcomings in the conventional rectangularlinear, matrix or capacitive micromachined ultrasonic transducer or“CMUT” arrays in order to maintain information from an extended phasedarray “in phase”, and to achieve a desired level of imaging lateralresolution.

In some embodiments, the ultrasound imaging system may be configured toallow for manual or automatic control of view angle, beam width andaperture size. This feature can be very advantageous when attempting toimage tissue obscured by gas, bone or other ultrasound-opaque structures(e.g. vertebrae, joints, peripheral vasculature, organs located insidethe thoracic cavity, etc.). With a shaped probe placed over the regionof interest, the sonographer may control view angle of the target. Oncethe desired view angle is selected, the sonographer may electronicallycontrol aperture width in order to achieve the best resolution at thedesired depth.

In one embodiment, there is a medical ultrasound apparatus having: (a)electronics configured for pulsing piezoelectric elements to transmitultrasonic waves into human (or animal) tissue; (b) electronicsconfigured to receive the resulting echo signals; (c) electronicsconfigured to process the echo signals to form images; and (d) a probehaving a plurality of receive elements within a receive subaperture,where the receive subaperture is sufficiently small that speed of soundvariations in the paths from scatterers to each of the receive elementsare sufficiently small to avoid phase cancelation when coherentaveraging is used based on the assumption of uniform speed of soundprofile over all paths. In addition, the probe may have a transmitelement or plurality of transmit elements within a transmit subaperture,with at least one of the transmit elements being separated from thereceive subaperture(s).

In another embodiment, the separation of transmit elements from elementsof a receive subaperture is imposed for the purpose of increasing thetotal aperture width which determines the lateral resolution of thesystem without making the receive subaperture so large that phasecancellation degrades the image.

In another embodiment, the transmit subaperture may be sufficientlysmall that speed of sound variations in the paths from the transmitelements to scatterers are sufficiently small that the differencesbetween the actual transmit times along these paths and the theoreticaltimes assuming a constant nominal speed of sound vary from each other bya substantially small amount. In some embodiments, an acceptablevariation in actual vs. theoretical travel times is less than one periodof the ultrasound pulse. In some embodiments, the imaging controlelectronics insonifies the tissue to be imaged with a single ping, andbeamforming and image processing electronics may form images by coherentaddition of images formed by each single ping. In other embodiments, thebeamforming and image processing electronics may form images byincoherent addition of images formed by each single ping.

Imaging transmit control electronics, beamforming electronics and imageprocessing electronics may be collectively referred to herein asmultiple aperture ultrasound imaging (or MAUI) electronics.

In still another embodiment, the MAUI electronics may form images byusing image alignment such as cross correlation to align images and thenadding the images incoherently.

In still another embodiment, the transmit aperture is not necessarilysmall and may include a receive subaperture. The MAUI electronics mayinsonify the tissue to be imaged with a single ping and may form imagesby incoherent addition of complete images formed by each single ping.Still further, the MAUI electronics may be configured to form images byusing cross correlation to align images and then adding the imagesincoherently. In another embodiment, the system controller may includethe processing capability where images formed with the different groupscan be averaged together to form images with reduced noise andartifacts.

The improvements described herein are applicable to a wide variety ofprobe types including, for example, a general radiology concavedmultiple aperture probe, a bracelet multiple aperture probe, a palmmultiple aperture probe, and an adjustable multiple aperture probe.

In other alternative embodiments, aspects of the present provide forusing unfocused pings for transmit, the transmit aperture can be muchwider than the receive aperture and can enclose it.

In additional embodiments, receive elements of only one aperture can beused to construct an image when a transmit pulse or wave comes from anelement or array of elements located outside and away from the receiveelements' aperture, without using speed of sound correction in order toachieve a coherently averaged image.

Although several embodiments herein are described with reference tomedical ultrasound imaging, the skilled artisan will recognize thatfeatures and advantages of the embodiments herein may also be achievedin non-medical ultrasound imaging applications, or in non-imagingapplications of ultrasound.

As used herein the terms “ultrasound transducer” and “transducer” maycarry their ordinary meanings as understood by those skilled in the artof ultrasound imaging technologies, and may refer without limitation toany single component capable of converting an electrical signal into anultrasonic signal and/or vice versa. For example, in some embodiments,an ultrasound transducer may comprise a piezoelectric device. In otherembodiments, ultrasound transducers may comprise capacitivemicromachined ultrasound transducers (CMUT).

Transducers are often configured in arrays of multiple individualtransducer elements. As used herein, the terms “transducer array” or“array” generally refers to a collection of transducer elements mountedto a common backing plate. Such arrays may have one dimension (1D), twodimensions (2D), 1.5 dimensions (1.5D) or three dimensions (3D). Otherdimensioned arrays as understood by those skilled in the art may also beused. Transducer arrays may also be CMUT arrays. An element of atransducer array may be the smallest discretely functional component ofan array. For example, in the case of an array of piezoelectrictransducer elements, each element may be a single piezoelectric crystalor a single machined section of a piezoelectric crystal.

A 2D array can be understood to refer to a substantially planarstructure comprising a grid of ultrasound transducer elements. Such a 2Darray may include a plurality of individual elements (which may besquare, rectangular or any other shape) arranged in rows and columnsalong the surface of the array. Often, a 2D array is formed by cuttingelement sections into a piezoelectric crystal.

As used herein, references to curved 1D, 1.5D or 2D transducer arraysare intended to describe ultrasound transducer arrays with curvedsurfaces having a curvature about only one axis (e.g., a transverse axisof a rectangular array). Thus, embodiments of 1D, 1.5D or 2D curvedarrays may be described as partial cylindrical sections.

As used herein, the term “3D array” or “3D curved array” may beunderstood to describe any ultrasound transducer array with a curvedsurface having curvature about two or more axes (e.g., both transverseand longitudinal axes of a rectangular array). Elements of a 3D curvedarray may be displaced relative to all adjacent elements in threedimensions. Thus, 3D curved arrays may be described as having a3-dimensional quadric surface shape, such as a paraboloid or a sectionof a spherical surface. In some cases, the term 3D array may refer tocurved CMUT arrays in addition to machined piezoelectric arrays.

As used herein, the terms “transmit element” and “receive element” maycarry their ordinary meanings as understood by those skilled in the artof ultrasound imaging technologies. The term “transmit element” mayrefer without limitation to an ultrasound transducer element which atleast momentarily performs a transmit function in which an electricalsignal is converted into an ultrasound signal. Similarly, the term“receive element” may refer without limitation to an ultrasoundtransducer element which at least momentarily performs a receivefunction in which an ultrasound signal impinging on the element isconverted into an electrical signal. Transmission of ultrasound into amedium may also be referred to herein as “insonifying.” An object orstructure which reflects ultrasound waves may be referred to as a“reflector” or a “scatterer.”

As used herein, the term “aperture” may refer to a conceptual “opening”through which ultrasound signals may be sent and/or received. In actualpractice, an aperture is simply a group of transducer elements that arecollectively managed as a common group by imaging control electronics.For example, in some embodiments an aperture may be a physical groupingof elements which may be physically separated from elements of anadjacent aperture. However, adjacent apertures need not necessarily bephysically separated.

It should be noted that the terms “receive aperture,” “insonifyingaperture,” and/or “transmit aperture” are used herein to mean anindividual element, a group of elements within an array, or even entirearrays with in a common housing, that perform the desired transmit orreceive function from a desired physical viewpoint or aperture. In someembodiments, such transmit and receive apertures may be created asphysically separate components with dedicated functionality. In otherembodiments, any number of send and/or receive apertures may bedynamically defined electronically as needed. In other embodiments, amultiple aperture ultrasound imaging system may use a combination ofdedicated-function and dynamic-function apertures.

As used herein, the term “total aperture” refers to the total cumulativesize of all imaging apertures. In other words, the term “total aperture”may refer to one or more dimensions defined by a maximum distancebetween the furthest-most transducer elements of any combination of sendand/or receive elements used for a particular imaging cycle. Thus, thetotal aperture is made up of any number of sub-apertures designated assend or receive apertures for a particular cycle. In the case of asingle-aperture imaging arrangement, the total aperture, sub-aperture,transmit aperture, and receive aperture will all have the samedimensions. In the case of a multiple aperture imaging arrangement, thedimensions of the total aperture includes the sum of the dimensions ofall send and receive apertures.

In some embodiments, two apertures may be located adjacent one anotheron a continuous array. In still other embodiments, two apertures mayoverlap one another on a continuous array, such that at least oneelement functions as part of two separate apertures. The location,function, number of elements and physical size of an aperture may bedefined dynamically in any manner needed for a particular application.Constraints on these parameters for a particular application will bediscussed below and/or will be clear to the skilled artisan.

Multiple aperture ultrasound imaging techniques can benefitsubstantially from the physical and logical separation of ultrasoundtransmitting and receiving functions. In some embodiments, such systemsmay also substantially benefit from the ability to receive echoessubstantially simultaneously at two or more separate receive apertureswhich may be physically spaced from a transmit aperture. Furtherbenefits may be achieved by using one or more receive apertures locatedon a different scan plane than elements of a transmit aperture.

Elements and arrays described herein may also be multi-function. Thatis, the designation of transducer elements or arrays as transmitters inone instance does not preclude their immediate redesignation asreceivers in the next instance. Moreover, embodiments of the controlsystem herein include the capabilities for making such designationselectronically based on user inputs, pre-set scan or resolutioncriteria, or other automatically determined criteria.

In some embodiments, each echo detected at a receive aperture may bestored separately in volatile or non-volatile memory within the imagingelectronics. If the echoes detected at a receive aperture are storedseparately for each pulse from the insonifying aperture, an entiretwo-dimensional image can be formed from the information received by asfew as just one element. Additional copies of the image can be formed byadditional receive apertures collecting data from the same set ofinsonifying pulses. Ultimately, multiple images can be createdsubstantially simultaneously from one or more apertures and combined toachieve a comprehensive 2D or 3D image.

Multiple Aperture Ultrasound Imaging (MAUI) methods and systems havebeen previously introduced in Applicants' prior US patent applicationsreferenced above. These applications describe multiple aperture imagingtechniques and systems including embodiments which consider eachindividual receive element as an independent aperture from which acomplete 2D image can be formed. Many such receive apertures can formmany reconstructions of the same 2D image but with different pointspread functions and different noise components. A combination of theseimages provides a vastly-improved overall image in terms of both lateralresolution and reduction of speckle noise.

As discussed in Applicant's previous applications, in order for theimages from multiple receive apertures to be combined coherently, therelative acoustic position of each element relative to the transmitelement(s) (or some other fixed coordinate system relative to the probe)must be known precisely to a desired degree of accuracy. Traditionally,the position of transducer elements is typically assumed to correspondto a geometric center of a structure forming an element. For example, inthe case of a conventional 1D phased array probe, the mechanicalposition of the elements may determined by the size of the cuts insidethe crystal wafer 110, in FIG. 6B. The acoustic center is generallyassumed to be at the center of the shaped crystalline structure; (e.g.,a parabolic channel running down the mid portion of the elements, 120,FIG. 6B).

However, the acoustic position of transducer elements may notnecessarily correspond exactly to their geometric or mechanicalpositions. Therefore, in some embodiments, the true acoustic position ofeach element in an array can be determined by a calibration system andprocess, as described in Applicants' previous applications.

Substantial imaging and practical use benefits may be achieved by usingmultiple aperture imaging processes with a concave curved ultrasoundtransducer array. In some embodiments, a concave transducer array mayhave a relatively large radius of curvature, as shown for example inFIG. 6. In other embodiments, as shown for example in FIG. 7 a concavetransducer array may have a relatively small radius of curvature. Insome embodiments, such a concave curvature may be substantiallycontinuous as shown, or a similar concave structure may be formed byjoining a plurality of linear segments. With adequate calibration,virtually any array shape may be formed and utilized.

Although the following embodiments are described with reference to asingle, continuous transducer array, the skilled artisan will recognizethat the same basic structures, features and benefits may be achieved byusing a plurality of separate transducer arrays, each of which may havea planar or curved shape as desired. Thus, it is to be appreciated thatany number of elements or blocks of arrays may be used in a multipleaperture probe using the systems and methods described herein.

As will be discussed in more detail below, in some embodiments, aconcave ultrasound imaging probe may be used in combination with imagingcontrol electronics having a number of unique adjustment and controlparameters. For example, by providing a substantially continuous concavecurved transducer array in combination with suitable controlelectronics, the physical location of transmit and/or receive aperturesmay be changed dynamically without moving the probe. Additionally, thesize and number of elements assigned to a transmit and/or receiveaperture may be changed dynamically. Such adjustments may allow anoperator to adapt a system for a broad range of variations in use andpatient physiology.

FIG. 1 illustrates an embodiment of a multiple aperture ultrasoundimaging system control panel configured for use with at least oneultrasound imaging array and a control system configured to drive andcontrol ultrasound imaging with the array(s). The control system can bereferred herein to as MAUI electronics, and can include such features asa computer processor, memory, a pulse generator, software configured tocontrol any attached ultrasound arrays. The MAUI electronics areillustrated throughout this application, and it should be understoodthat the various embodiments of ultrasound arrays illustrated herein caneach be driven and controlled by MAUI electronics. In some embodiments,a MAUI control panel may include aperture controls such as an apertureview angle control 410 and an aperture width control 420. A MAUI controlpanel may also include element controls 430 and 440 configured to adjustthe number of elements used for each transmit aperture and each receiveaperture, respectively. In some embodiments, the controls 410, 420, 430,440 may include buttons, knobs, scroll wheels, trackballs, touch pads,sliders or any other suitable human interface device.

FIG. 2 illustrates one embodiment of a concave curvilinear array ofultrasound transducer elements during a single multiple apertureultrasound imaging cycle. In this illustration, one or more elements ina transmit aperture T₁ are shown transmitting energy into a medium.Transmit beamforming may utilize either a phased array or be a simpleping. In either case, energy is transmitted toward region of interestwhich has at least one reflector 170. Receive aperture elements R₁ maybe electronically designated to collect data for this transmit cycle bythe MAUI Electronics 140.

Based on calibrated acoustic position data defining the position of eachelement, individual distances of all receive elements in R₁ from theelement(s) of the transmit aperture T₁ for this capture period may becomputed in firmware or hardware. This allows data from the receiveaperture R₁ to be assembled into an aligned image in real timeimmediately upon receipt. Image compounding or post processing is notrequired and may be omitted.

The size (e.g. width) of the single aperture of a conventional phasedarray probe, and hence the resolution, can be severely limited by thevariation of speed of sound in the tissue between the transducer and theorgan of interest. Although speed of sound in various soft tissuesthroughout the body can vary by +/−10%, it is usually assumed that thespeed of sound is constant in the path between the transducer and theorgan of interest. This assumption is valid for narrow transducer arraysin systems using one transducer array (e.g., a single array used forboth transmit and receive). However, the constant speed of soundassumption breaks down as the probe's total aperture becomes widerbecause the ultrasound pulses pass through more tissue and possiblydiverse types of tissue. Tissue diversity under the length of thetransducer array may affect both the transmit and the receive functions.

When a reflector such as reflector 170 in FIG. 2 is insonified by eithera focused pulse from a group of transmit elements or a ping from asingle transmit element, the reflector 170 reflects an echo back to allof the elements of a designated receive aperture R₁. Coherent additionof images collected by elements in this receive aperture can beeffective if the speed of sound variations in the paths from reflector170 to each of the receiver elements in R₁ do not exceed +−180 degreesphase shift relative to one path chosen as reference.

The maximum physical size of the aperture R₁ for which coherent additioncan be effective is dependent on tissue variation within the patient andcannot be computed accurately in advance. Conventional ultrasoundimaging systems are typically designed with an aperture width that is acompromise for a wide range of possible patients, studies and viewangles so as to avoid phase conflicts for a wide range of expected uses.However, because they involve compromise, such conventional probes donot necessarily produce an optimum image. Phase coherence is equallyimportant when using a group of elements to generate a focused transmitbeam, and again is often a compromise in conventional transducer arraywidths and operation.

Thus, in some embodiments, the size (e.g., width in terms of number ofdesignated elements) of transmit and/or receive apertures may becontrolled either automatically or manually using controls such as themultiple aperture ultrasound imaging system control panel shown inFIG. 1. Adjusting the aperture size may allow the operator to find thebest aperture for each individual patient. In alternative embodiments,an optimum aperture size may be found automatically by programming thecontrol electronics to rapidly try several array sizes and pick the oneyielding best image acuity (e.g. sharpness, high frequency content).Thus, in some embodiments, a control panel may include button or othercontrol to initiate such an automatic aperture-size-determinationprocedure. In some embodiments, such aperture size adjustments may beapplied to a total aperture size for a probe or application.Alternatively or in addition, such aperture size adjustments may beapplied to individual transmit or receive apertures.

An optimum receive aperture size for a particular patient or applicationmay be determined electronically or controlled manually. The optimumaperture is the aperture size that retains the best signal to noiseratio while still in phase. An aperture that is too wide will lose oneor both of these qualities, and degrade the image. Therefore in someembodiments, the sonographer may control the size of the group ofreceiver elements used for each receiver group R₁ in FIG. 2 bymanipulating controls 410, 420, 430 and 440 until he/she sees no furtherimprovement in image quality. In another embodiment, a controller in theMAUI electronics 140 can be configured to automatically select the sizeof the group of receiver elements used for receiver group R₁ bydetermining the best signal to noise ratio while still in phase.

The size of the group of transmitter elements T₁ depends on whether thetransmitted pulse is a focused beam formed from the phased firing of agroup of transducer elements or an unfocused pulse from just one or afew elements at a time. In the first case, the transmit aperture sizemay be limited to the same size as the optimum receive aperture size. Inembodiments using unfocused pings, the transmit aperture size is muchless critical since variation in the path time from transmitter elementsto a reflector such as 170 will change only the displayed position ofthe point corresponding to the reflector 170. For example, a variationresulting in a phase shift of 180 degrees in the receive paths resultsin complete phase cancellation, whereas the same variation on thetransmit paths results in a displayed position error of only a halfwavelength (typically 0.2 mm), a distortion that would typically not benoticed.

Thus, with continued reference to FIG. 2, the speed of sound along thepaths from element(s) of the transmit aperture T₁ to the reflector 170need not be accounted for in the coherent addition of the receivedsignals. The aperture size of the receiver group R₁, on the other hand,may be as large as for a conventional phased array (e.g. about 2 cm) insome embodiments. But unlike a conventional array, the total aperture190 (e.g. the maximum distance from the furthest-left transmit elementof T₁ to the furthest-right receive element of R₁ in the FIG. 2embodiment) determining the lateral resolution of the system is muchlarger.

A single image can be formed by coherent averaging of all of the signalsarriving at the receiver elements as a result of a single insonifyingping. Summation of these images resulting from multiple pings may beaccomplished either by coherent addition, incoherent addition, or acombination of coherent addition by groups and incoherent addition ofthe images from the groups. Coherent addition (retaining the phaseinformation before addition) maximizes resolution whereas Incoherentaddition (using the magnitude of the signals and not the phase)minimizes the effects of registration errors and averages out specklenoise. Some combination of the two modes is probably best. Coherentaddition can be used to average ping images resulting from transmitelements that are close together and therefore producing pulsestransmitted through very similar tissue layers. Incoherent addition canthen be used where phase cancellation would be a problem. In the extremecase of transmission time variation due to speed of sound variations, 2Dimage correlation can be used to align ping images prior to addition.

The wide aperture achieved by separating the transmit and receiveapertures is what allows for the higher resolution imaging associatedwith Multiple Aperture Ultrasound Imaging (MAUI). However, this wideaperture does not by itself reduce another significant detractor ofultrasound imaging; speckle noise.

Speckle noise patterns are associated with the transmit source. That is,during receive beamforming, the speckle noise pattern from a steadystate phased array or ping transmit source appear as constant “snow” inthe displayed image as long as the probe or tissue being imaged is notturned or moved significantly during imaging. If the probe is moved ortwisted, the speckle noise or “snow” on the image will obscure a newportion of the image. Hence, data collected at a single receive aperturefrom transmissions from alternate transmit apertures will subsequentlyhave many different speckle noise patterns.

In the embodiment illustrated in FIG. 2 data collected at receiveaperture R₁ is coming from a single transmit source T₁, and thereforewill have a singular consistent speckle noise pattern. By itself, thisis the same limiting factor of conventional ultrasound today. However,by initiating a second insonification from the reciprocal positionsT_(1R) and R_(1R) of FIG. 2A upon the completion of the first imagecapture, a second image may be obtained almost immediately. This secondimage (from transmit source T_(1R)) will have a different speckle noisepattern than the first (from transmit source T₁). Thus, by combining thetwo images, both speckle noise patterns may be substantially identifiedand eliminated. The ability to invert the roles of transmitter andreceiver in array elements produces differing noise patterns which willsubstantially cancel each other out once combined. The result of thisarray role reversal is a much clearer ultrasound image while stillmaintaining the same high resolution from the wider total aperture 190.

FIG. 2B demonstrates an embodiment in which a concave curved multipleaperture array cycles through a number of different views of the regionof interest 170. The advantage of this process is to gain sequentialimages of the same target and then combine the images for a morecomprehensive presentation to the sonographer. In this case, the MAUIElectronics 140 may simply cycle through a programmable sequence oftransmit and receive apertures across the entire width of the array orcollective arrays while maintaining a fixed maximum total aperturewidth.

In some embodiments, an array of this type may be configured to includetransmit and receive elements with different frequency rangesinterspersed in the array. As an example, T₁ and R₁ could be tuned to 2MHz, T₂ and R₂ could be tuned to 5 MHz, and T₃ and R₃ could be tuned to10 MHz. This technique would further reduce speckle noise in the images.

FIG. 2B also demonstrates another unique feature of some embodiments ofmultiple aperture arrays called view angle control. The view angle maybe defined as the angle α between lines 180 and 190 that could be drawnfrom T₁ to 170 and from R₁ to 170. In some embodiments, the MAUIelectronics 140 may be configured to automatically move the transmit T1and receive R1 apertures along the array or arrays without changing thetotal distance between the transmit T₁ and receive R₁ apertures. Inother embodiments, the transmit and receive apertures can be movedmanually, such as with the view angle control 410 of FIG. 1.

In some embodiments, further improvements of the images can sometimes beobtained by rapidly changing the positions of the groups (includingswitching the designations of the groups relative to transmit andreceive functions) and adding the resulting images incoherently.

An array placed near a physiology that creates an obstruction (e.g. avertebrae, rib, wrist bone, etc.) would not be able to combine orcompound a complete image. With a conventional probe, a sonographerwould physically move the probe on the patient's skin to obtain a clearultrasound window. However, with a dynamic multiple aperture ultrasoundprobe, the view angle of the probe can be adjusted to compensate for anobstruction in the field of view. For example, if the view created by T₂and R₂ is obstructed by a bone or other obstruction 150, then the MAUIelectronics 140 can automatically rotate that view angle over to T₁ andR₁, or alternatively to T₃ and R₃, until the region of interest isun-obscured. In other embodiments, this technique can be performedmanually by a sonographer.

FIG. 2C illustrates another important capability of some embodiments ofmultiple aperture arrays, referred to herein as total aperture sizecontrol. In this embodiment, the view angle created by T_(1A) and R_(1A)provides an obstruction-free view of the region of interest includingreflector 170 which avoids obstruction 150. In this example, the systemis providing multiple aperture imaging with a total aperture width ofA_(1A.). Using total aperture size control, the total aperture width canbe varied either inward or outward on the array, while maintaining afixed view angle center. Thus, in some embodiments, as a total aperturesize is adjusted, both transmit and receive apertures may beelectronically moved at the same rate outward or inward from the fixedview angle center so as to maintain the original view angle.

Radian resolution is proportional to λ/d, where λ is wavelength and d istotal aperture width. The wider the total aperture, the higher theresolution; the smaller the total aperture, the lower the resolution.The total aperture width can be varied to get the best possibleresolution for a chosen view angle. For example, in the embodiment ofFIG. 2C, the total aperture width can be maximized by selecting thetotal aperture width between T_(1B) and R_(1B), resulting in a totalaperture width of A_(1B).

In additional embodiments, data may be collected at multiple receiveapertures for a single transmit pulse, as illustrated in FIGS. 3 and 3A.Data collection in this fashion provides the added benefit of increasedaperture width A₁ during real time data collection.

In FIG. 3, total aperture width A₁ is determined by the distance betweenthe outer most elements of receive apertures R₁ and R₂. In FIG. 3A, thetotal aperture width A₁ is determined by the distance between the outermost elements of transmit aperture T₁ and receive aperture R₂. Sincemultiple apertures are being used in the receive beamformersimultaneously, higher resolution can be attained in real time. Thiscapability allows for precise data capture on moving objects, likecoronary valves.

However, unlike embodiments using only a single receive aperture,multiple receive aperture beamforming often requires a speed of soundcorrection to accommodate differing tissue attenuation speeds situatedalong multiple “lines of sight” to the region of interest (e.g.,referring to FIGS. 3 and 3A, a first line of sight being from reflector170 to R₁, and a second line of sight being from reflector 170 to R₂).This calculation should be made if data collected nearly simultaneouslyfrom different receive apertures is to be coherently combined.Embodiments of techniques and methods for such speed of soundcorrections are described in Applicants' prior patent applicationsreferenced above.

The examples in FIGS. 2-3A demonstrate embodiments of multiple apertureimaging using a multiple aperture array or arrays with elements that arealigned within the same scan plan. Such arrays may be 1D, 1.5D, or 2D orCMUT concave curved arrays. 3D volumes can be constructed by piecingtogether 2D slices generated using such systems into a 3D volume. Thisis a post processing function, so data from a 1D multiple aperture arraycannot image 3D data in real time (also known as 4D imaging).

Embodiments of concave curved arrays of 1.5D, 2D, 3D and CMUT transducerarrays have more capabilities which will now be examined. Such arraysmay have concave curvature about one or two or more axes. Although manyof the following embodiments are described with reference to arrayshaving curvature about two axes, similar methods may be applied usingtransducer arrays having curvature about only one axis.

FIG. 4 illustrates a concave 3D transducer array 300 having curvatureabout two orthogonal axes. In some embodiments, a 3D concave curvedarray 300 may be constructed using machined piezoelectric transducers.In other embodiments, the array 300 may be constructed using CMUTtransducers such as those illustrated in FIGS. 6C, 7E or 8E. Calibrationof a 3D array may be needed as each element of the array will haveslightly different positions in the x axis 301, y axis 302 and z axis303.

In some embodiments, calibration data including element positioninformation may be stored in a calibration chip onboard each MAUI probeso that it can be used by MAUI electronics during processing. In otherembodiments, calibration data including element position information maybe stored in a remote database which may be accessed electronically bycommunications components within the probe or within an ultrasoundimaging system. For example, calibration data may be stored in anInternet-accessible database which may be accessed by an ultrasoundimaging system. In such embodiments, the probe may include a chipstoring a unique identifier which may be associated with correspondingcalibration data in a remote database.

In the illustration of FIG. 4, a snap shot of multiple aperture datacollection is depicted en route to building an image of an entire volume310. Here, an element or elements of a transmit aperture T₁ transmit apulse into the volume that includes scatterers such as 321 and 322. Theelements making up receive aperture R₂ may be assembled in a variety ofshapes. Here, a square of elements makes up the receive apertures R₂ andR₃. As mentioned above, the speed of sound along the path from thetransmit aperture T₁ to the reflector 321 or 322 is irrelevant to thecoherent addition of the received signals as long as a single apertureis used to receive, however, speed of sound corrections can be made toimprove image quality when using multiple receive apertures R₁ and R₂.

In some embodiments, the size of the receive aperture R₂ may be as largeas for a conventional phased array (e.g., about 2 cm). But unlike aconventional array, the total aperture 340 determining the lateral andtransverse resolution of the system is much larger comprising thedistance from the transmitter T₁ to the group of receiver elements R₂,and could be as wide as the entire array 300 or wider if a transmitterwas located on another array within the probe (or in a separate probe inelectronic communication). The elements located in the receive apertureR₂ each collect volumetric data from the T₁ transmit pulse. Since aspeed of sound correction is not required for data collected from asingle transmit pulse at a single aperture, data from each element of R₂may be coherently averaged with the other elements in pre-processing.

A speed of sound correction may or may not be required for averagingvolume renderings for multiple pulses depending on the size of thetransmit aperture (i.e. a total distance between furthest elements of atransmit aperture). If the transmit aperture is small enough that thetransmit elements transmit through substantially the same types oftissue, coherent addition may still be possible. If the transmitaperture is larger, a speed of sound correction in the form ofincoherent addition may be required.

If the transmit aperture is large enough that the transmit elements arestill farther apart, the correction may take the form of incoherentaddition of echoes received at each element, but alignment may beaccomplished by cross correlation or some form of adjustment to maximizeacuity, such as adjustment of the view angle, individual aperture sizeand/or total aperture size. A 3D concave array may provide mechanicallybetter view angles of a region of interest than conventional coplanar 2Darrays because of its concave curvature and width.

In some embodiments, a 3D array may also image tissues of varyingdensity. FIG. 4 illustrates a second receive R₃ aperture that can beused simultaneously with R₂ during a single transmit pulse from atransmit aperture T₁. However, unlike the single receive aperturesituation, multiple receive aperture beamforming may require a speed ofsound correction to accommodate differing tissue attenuation speedssituated along multiple “lines of sight” to the region of interest.

In this case, the elements located in aperture R₃ may collect volumetricdata from the T₁ transmit pulse. Again, since a speed of soundcorrection is not required for echoes received by multiple elements ofthe single receive aperture R₃, data from each element in R₃ may becoherently averaged with the other elements of R₃ in pre-processing.

Volumes for R₂ and R₃ may be stored in memory and may then beincoherently averaged with one another to create a single 3D volume.While only receive apertures R₂ and R₃ are illustrated here, any numberof receive apertures can be used. In some embodiments, receive aperturesmay use the entire array 300 as a total aperture. Using multiple receiveapertures greatly reduces noise as well as increases total aperture sizeto provide higher resolution.

Like 2D multiple aperture imaging, the 3D multiple aperture imaging madepossible by a 3D concave curved array may use many transmit apertures.Even with a 3D array, the noise patterns associated with T₁ will have asingular consistent speckle noise pattern. FIG. 4A demonstrates transmitpulses from multiple apertures T₁ through T_(N). In the illustratedcase, alternate transmit locations may be utilized, but only a singlereceive aperture R₂ is used so speed of sound corrections are notneeded. Data collected at R₂ can be coherently averaged for each elementin that receive aperture and subsequently for each transmit pulse, andfinally placed into memory. Once all transmit pulses are completed,volumetric data may be incoherently combined. Data from the differingtransmit elements will produce differing noise patterns that will canceleach other out once combined to provide a much clearer 3D ultrasoundimage.

FIGS. 4B and 4C illustrate a 3D array being using to collect a 2D sliceof data. In the case of FIG. 4B, the slice 320 is along the longitudinalaxis of the array. In the case of FIG. 4C, the slice 330 is along thetransverse axis of the array. 2D slices may also be obtained at anyother angle relative to the probe. In some embodiments, the probe mayuse a partial line of elements to create transmit aperture T₁. In someembodiments, elements may be energized in phase to focus a beam onto theplane 320 in FIG. 4B or the plane 330 in FIG. 4C. In these cases, theelements of T₁ may be narrow so that the energy is unfocused in thedirection of the plane. The length of the partial line of elements in T₁may be chosen to be long enough to focus the width of the plane.

Referring again to FIGS. 4B and 4C, receive aperture R₂ can be usedsingularly to collect data for longitudinal slice 320. The elementslocated in aperture R₂ each collect data from the T₁ transmit pulse.Since a speed of sound correction is not required for this type ofcollection, data from each element may be coherently averaged with theother elements in pre-processing. Subsequently, transmitter groups T₁,T₂ . . . T_(N) may each be fired to insonify the plane 320 (or 330),each with a different x (or z) position. Partial images of the plane maythen be combined either coherently or incoherently with the sameconsiderations as discussed with respect to the embodiments discussedabove with reference to FIGS. 2 and 3.

As discussed above, the view angle and total aperture width can beadjusted. In some embodiments, the view angle may be adjusted in anydesired direction along the 3D array.

With a 3D concave array, a 2D slice angle adjustment may also beprovided to allow for selection of a 2D slice to be imaged withouthaving to rotate a probe. A 2D slice angle adjustment may effectivelyallow rotation of a 2D slice around the y axis to obtain a 2D slice atany angle between that of FIG. 4B and that of FIG. 4C. Similaradjustment may also be provided to allow for a selected 2D slice to berotated about the x or z axes.

Thus, the arrays described herein may provide an enormous range offlexibility in selecting and optimizing a 2D image without necessarilymoving the probe at all. A 3D array provides mechanically better viewangles of the region of interest than conventional coplanar 2D arraysbecause of its concave curvature and greater total width.

FIGS. 4D and 4E demonstrate embodiments of a 3D curved array being usedfor data collection of 3D volumetric data, alternating with a 2D highresolution slice. The sonographer can use a 3D display containing aselectable 2D longitudinal and axial reference line. When in theside-by-side display mode, the 3D image can show the entire volume, anda multiple aperture 2D image can display a high resolution slice for thereference line selected. This is made possible by the array being ableto switch between ping transmit from individual elements for volumetricimaging to a shaped pulse transmit (either longitudinally or axially)for 2D slice data for a desired axis. The 2D slice data receives thebenefit of concentrated multiple aperture receiving beamforming on asingle slice.

Several embodiments of multi-aperture arrays and their unique transducerhousings are described below with reference to FIGS. 5-8E. Theseexamples represent some of the flexibility in ultrasound probe designand fabrication that may be achieved when using multi-aperturetechniques. The following embodiments provide examples of some generalclasses of probes (e.g. concave arrays, 3D arrays, conformal andadjustable arrays); however, because of the flexibility in arrayconfiguration, a multiple aperture array allows for many conceivableprobes to be constructed that are not illustrated here.

FIG. 5 illustrates one embodiment of a general radiology ultrasoundprobe with a continuous concave curved transducer array. This probe maybe operated according to any of the methods described herein. The radiusof curvature of this array may be selected to be sufficiently shallow toallow for imaging a variety of body tissues (e.g., abdomen, pelvis,peripheries, etc.). In some embodiments, the concave probe of FIG. 5 maybe used to image in 2D as a curvilinear probe using a 1D array such asthat shown in FIG. 5A. The probe of FIG. 5 may also operate in 3D or 4Dimaging modalities using a 3D piezoelectric array such as that shown inFIG. 5B or a CMUT array such as that illustrated in FIG. 5C.

In some embodiments, a concave array such as that shown in FIG. 5 may besubstantially rigidly mounted in a probe. Such an array may be held inplace by a backing plate 508. In some embodiments, a single flexconnector 505 may be used to electronically connect elements of thetransducer array to a cable to be connected to an ultrasound imagingsystem. In some embodiments, a concave array probe may also include atransmit synchronizer module 502 and probe position displacement sensor503. In some embodiments, a transmit synchronization module 502 may beused for identifying the start of a transmit pulse when the probe isused as an add-on device with a host machine transmitting. A probedisplacement sensor 503 may be an accelerometer, gyroscope or othermotion-sensitive device that senses movement of the probe.

A Calibration Chip 501 may also be provided within the probe. In someembodiments, a calibration chip 501 may store calibration datadescribing the acoustic position of each transducer element asdetermined during a probe calibration process. In some embodiments, thecalibration chip 501 may include non-volatile memory for storing suchcalibration data. The calibration chip 501 or another component withinthe probe may also include communication electronics configured totransmit calibration data to an ultrasound imaging system.

FIG. 6 is another embodiment of an ultrasound probe with a concave arrayhaving significantly smaller radius of curvature than the probe of FIG.5. In some embodiments, the probe of FIG. 6 may be sized and configuredto partially surround a joint or extremity. In some embodiments, thecurvature of this array may allow a sonographer to image structuresbehind bone or other obstructions as discussed above with reference toFIGS. 2B and 2C. Similarly, the probe of FIG. 6 may be used to isolateareas of interest by manually or automatically adjusting the positionand/or size of transmit and/or receive apertures without moving theentire probe.

In some embodiments, the concave array probe of FIG. 6 may be used toimage in 2D as a curvilinear probe using a 1D array such as that shownin FIG. 6B. The probe can also operate in 3D or 4D imaging modalitiesusing a 3D piezoelectric array such as that illustrated in FIG. 6C or aCMUT array such as that illustrated in FIG. 6D. Using methods describedherein, the probe of FIG. 6 may be used to produce a complete 3Dtomographic display of an extremity or joint while a sonographer holdsthe probe in one position. Such functionality is not possible withconventional ultrasound imaging arrays. In contrast, a conventionalarray must be moved around the joint, and images taken from a variety ofview angles must be compounded together for a 3D presentation. Becauseof the incongruences of imaging with a coplanar array and manualmovement, a tomographic 3D display from a conventional array istypically not physiologically contiguous.

In some embodiment, the probe of FIG. 6 may be constructed substantiallysimilarly to the probe of FIG. 5. For example, the transducer array(s)may be rigidly mounted to the probe and held in place by a backing plate508, and may include a flex connector 505. FIG. 6A illustrates anembodiment of a bracelet multiple aperture probe, which may besubstantially similar to the probe of FIG. 6, except that the cableconnector exits from a side or bottom section of the probe housing. Theembodiments of FIGS. 6 and 6A may also include transmit synchronizermodules 502, probe position displacement sensors 503, Calibration Chips501 and other features discussed elsewhere herein.

FIG. 7 illustrates an embodiment of a general radiology probe configuredto fit into the palm of a sonographer's hand. The probe of FIG. 7 mayinclude a curved array such as those shown in FIGS. 5 and 6. The probeof FIG. 7 is made possible by the ability to construct and calibrate aconcave ultrasound transducer array. Probes such as this maysignificantly reduce ergonomic strain on sonographers. The probe of FIG.7 may also be constructed with a substantially limited elevation orthickness (e.g., as shown in FIG. 7B). Such reduced thickness may allowa sonographer to reach in behind or underneath patients that cannot bemoved and still achieve an image over the areas of interest.

In some embodiments, the probe of FIG. 7 may include an adjustable handsupport for either right or left handed use. In some embodiments, thehand support may be configured to rotate relative to the probe body toallow the sonographer more flexibility. For example, FIG. 7 illustratesthe probe with the hand support in a longitudinal orientation, and FIGS.7A and 7B show the probe with the hand support rotated to a transverseposition.

In some embodiments, the radius of curvature of the array in the probeof FIG. 7 may be adequately shallow to allow for imaging a variety ofbody tissues (e.g. abdomen, pelvis, peripheries, etc.). The probe ofFIG. 7 can image in 2D as a curvilinear probe using a concave 1D arraysuch as that shown in FIG. 7C. The probe of FIG. 7 may also be operatedin 3D or 4D imaging modalities using a 3D piezoelectric array such asthat shown in FIG. 7D or a CMUT array such as that shown in FIG. 7E.

FIG. 7F illustrates an embodiment of a 3D piezoelectric or CMUT arraythat may be used to collect cylindrical volumes of data. The array ofFIG. 7F may be operated according to the methods discussed above withreference to FIGS. 4A-4E.

In some embodiments, the probe of FIG. 7F may be configured and/orcontrolled to function as an annular array in which transducer elementsare fired in concentric patterns to improve imaging depth.

As shown in FIG. 7G, embodiments of probes such as that shown in FIGS.7-7G may be constructed substantially similarly to probes discussedabove with reference to FIGS. 5 and 6. For example, the FIG. 7 probe mayinclude a backing plate 508, a flex connector 505, transmit synchronizermodule 502, a probe position displacement sensor 503, a Calibration Chip501, and any other suitable components.

FIG. 8 illustrates one embodiment of an adjustable probe with aplurality of adjustable ultrasound arrays that may be adjusted toconform to a variety of surface shapes. For example, a sonographer mayplace the adjustable probe around a physiology of interest, allowing thearrays to conform to the shape of the structure. The sonographer maythen lock the arrays into the conformed orientations. Once the arraysare locked in a desired orientation, the probe may be calibrated using asuitable calibration system and the probe may be used to image thephysiology of interest.

FIG. 8 illustrates one embodiment of an array adjustment and lockingmechanism. Many other mechanical adjustment and locking mechanisms mayalternatively be used. The mechanism of FIG. 8 includes a bellows 810configured to provide positive pressure on the five adjustable arrays812, biasing the arrays toward the orientation shown in FIG. 8. Thebacking blocks 504 of each of the adjustable arrays may be connected toeach other by hinge mechanisms 820. As the sonographer places pressureon the probe to overcome the resistance of the bellows, the arraysconform to the shape of the desired physiology as illustrated in FIG.8A.

At this time, the sonographer may turn the tightening handle 830 to lockall of the hinge mechanisms in place. The tightening handle may beconnected to the hinge mechanisms 820 via hinge cables 840. The cables840 may comprise an outer conduit 850 and an inner tension wire 860 asillustrated in FIG. 8B. The wire 860 may be attached to a pivot pin 870,and configured such that when the locking ring 830 is rotated, the wire860 drawn upwards, compressing the pivot pin 870 and hinge 820 for theentire length of the hinge. When the conformed position no longerneeded, the tightening handle may be relaxed and the bellows may pushall of the arrays out to their fully extended position.

In some embodiments, each array 812 in the adjustable probe may have itsown backing block 504 and flex connector 505. The type of arrays used inan adjustable array can vary. For example, FIG. 8C illustrates anadjustable probe with 1D probes. In some embodiments, an adjustableprobe may include transducer arrays of different frequencies. Forinstance, in some embodiments arrays that use lower frequencies may belocated on lateral ends of the probe, and arrays using higherfrequencies may be located towards the center. 2D or CMUT arrays mayalso be used, as shown in FIGS. 8D and 8E. In some embodiments, eacharray 812 of an adjustable probe may have a planar shape. In otherembodiments, each array 812 may have a concave shape with curvature inone or two or more axes.

An adjustable probe may include similar electronic components to otherstatic-position probes described herein. For example, an adjustableprobe may include a Calibration Chip 501, a transmit synchronizer module502 and probe position displacement sensor 503.

An adjustable probe such as that shown in FIG. 8 may be operated in 2D,3D or 4D imaging modalities according to any of the methods describedherein.

Terms such as “optimized,” “optimum,” “precise,” “exact” and similarterms used in relation to quantitative parameters are merely intended toindicate design parameters which may be controlled or varied inaccordance with general engineering principles. Use of these terms isnot intended to imply or require that the parameters or componentsthereof are designed for the best possible or theoretical performance.

The above disclosure is sufficient to enable one of ordinary skill inthe art to practice the invention, and provides the best mode ofpracticing the invention presently contemplated by the inventor. Whilethere is provided herein a full and complete disclosure of the preferredembodiments of this invention, it is not desired to limit the inventionto the exact construction, dimensional relationships, and operationshown and described. Various modifications, alternative constructions,changes and equivalents will readily occur to those skilled in the artand may be employed, as suitable, without departing from the true spiritand scope of the invention. Such changes might involve alternativematerials, components, structural arrangements, sizes, shapes, forms,functions, operational features or the like.

1. An ultrasound imaging system, comprising: an ultrasound transducerarray, the ultrasound transducer array having a concave curvature aboutat least one axis; a first transmit aperture in the ultrasoundtransducer array configured to insonify a scatterer with ultrasoundenergy; a first receive aperture in the ultrasound transducer arrayconfigured to receive ultrasound echoes from the scatterer, the firstreceive aperture being located apart from the first transmit aperture;and a control system in electronic communication with the ultrasoundtransducer array, the control system configured to access calibrationdata describing a position and orientation of the first transmitaperture and the first receive aperture, the control system configuredto form an ultrasound image with the echoes received by the firstreceive aperture.
 2. The system of claim 1 further comprising: a secondreceive aperture in the ultrasound transducer array configured toreceive echoes from the scatterer, the second receive aperture beinglocated apart from the first transmit aperture and the first receiveaperture; wherein the control system is configured to access calibrationdata describing a position and orientation of the second receiveaperture, and wherein the control system is configured to form anultrasound image with the echoes received by the first and secondreceive apertures.
 3. The system of claim 1 wherein the ultrasoundtransducer array has a concave curvature about at least two axes.
 4. Thesystem of claim 1 wherein the calibration data is stored in the controlsystem.
 5. The system of claim 1 wherein the calibration data is storedremotely from the control system.
 6. The system of claim 1 wherein thecalibration data is stored in a chip housed within a probe housing alongwith the array.
 7. A method of ultrasound imaging, comprising:transmitting ultrasound energy towards a scatterer with transmitaperture on an ultrasound transducer array having a concave curvatureabout at least one axis; receiving ultrasound echoes from the scattererwith a first receive aperture on the ultrasound transducer array;obtaining calibration data containing a position and orientation ofultrasound transducers in the first transmit aperture and the firstreceive aperture; and forming an ultrasound image with the ultrasoundechoes received by the first receive aperture.
 8. The method of claim 7further comprising: receiving ultrasound echoes from the scatterer witha second receive aperture on the ultrasound transducer array; obtainingcalibration data containing a position and orientation of ultrasoundtransducers in the second receive aperture; and forming an ultrasoundimage with the ultrasound echoes received by the first and secondreceive apertures.
 9. An ultrasound imaging system, comprising: anultrasound transducer array; a first transmit aperture in the ultrasoundtransducer array configured to insonify a scatterer with ultrasoundenergy; a first receive aperture in the ultrasound transducer arrayconfigured to receive ultrasound echoes from the scatterer, the firstreceive aperture being located apart from the first transmit aperture; asecond receive aperture in the ultrasound transducer array configured toreceive ultrasound echoes from the scatterer, the second receiveaperture being located apart from the first transmit aperture and thefirst receive aperture; and a control system in electronic communicationwith the ultrasound transducer array, the control system configured tochange a total aperture size of the system by switching from receivingechoes with the first receive aperture to receiving echoes with thesecond receive aperture.
 10. The system of claim 9 wherein the controlsystem is configured to access calibration data describing a positionand orientation of the first transmit aperture, the first receiveaperture, and the second receive aperture, wherein the control system isconfigured to form an ultrasound image with the echoes received by thefirst and second receive apertures.
 11. The system of claim 9 whereinthe control system is configured to change the total aperture sizeautomatically upon detection of an obstruction.
 12. An ultrasoundimaging system, comprising: an ultrasound transducer array; a firsttransmit aperture in the ultrasound transducer array configured toinsonify a scatterer with ultrasound energy; a second transmit aperturein the ultrasound transducer array configured to insonify the scattererwith ultrasound energy; a first receive aperture in the ultrasoundtransducer array configured to receive ultrasound echoes from thescatterer, the first receive aperture being located apart from the firsttransmit aperture; a second receive aperture in the ultrasoundtransducer array configured to receive ultrasound echoes from thescatterer, the second receive aperture being located apart from thefirst transmit aperture and the first receive aperture; and a controlsystem in electronic communication with the ultrasound transducer array,the control system configured to change an aperture view angle of thesystem by switching from transmitting ultrasound energy with the firsttransmit aperture to transmitting ultrasound energy with the secondtransmit aperture, and switching from receiving echoes with the firstreceive aperture to receiving echoes with the second receive aperture,wherein a transmit/receive angle between the first transmit aperture andthe first receive aperture is approximately the same as thetransmit/receive angle between the second transmit aperture and thesecond receive aperture.
 13. The system of claim 12 wherein the controlsystem is configured to access calibration data describing a positionand orientation of the first transmit aperture, the first receiveaperture, and the second receive aperture, wherein the control system isconfigured to form an ultrasound image with the echoes received by thefirst and second receive apertures.
 14. The system of claim 12 whereinthe control system is configured to change the aperture view angleautomatically upon detection of an obstruction.
 15. A method ofultrasound imaging, comprising: transmitting ultrasound energy towards ascatterer with a first transmit aperture on an ultrasound transducerarray having a concave curvature about at least one axis; receivingultrasound echoes from the scatterer with a first receive aperture onthe ultrasound transducer array; detecting an obstruction between thescatterer and the first receive aperture; and after detecting theobstruction, receiving ultrasound echoes from the scatterer with asecond receive aperture on the ultrasound transducer array.
 16. Themethod of claim 15 wherein the detecting step is performed by asonographer.
 17. The method of claim 15 wherein the detecting step isperformed automatically by a control system.
 18. The method of claim 15wherein the transducer array has a concave curvature about at least twoaxes.
 19. The method of claim 15 wherein the after detecting stepfurther comprises: after detecting the obstruction, receiving ultrasoundechoes from the scatterer with the second receive aperture on theultrasound transducer array, wherein the obstruction is not locatedbetween the scatterer and the second receive aperture.
 20. A method ofultrasound imaging, comprising: transmitting ultrasound energy towards ascatterer with a first transmit aperture on an ultrasound transducerarray having a concave curvature about at least one axis; receivingultrasound echoes from the scatterer with a first receive aperture onthe ultrasound transducer array; detecting an obstruction between thescatterer and the first transmit aperture; and after detecting theobstruction, transmitting ultrasound energy towards the scatterer with asecond transmit aperture on the ultrasound transducer array.
 21. Themethod of claim 20 wherein the detecting step is performed by asonographer.
 22. The method of claim 20 wherein the detecting step isperformed automatically by a control system.
 23. The method of claim 20wherein the transducer array has a concave curvature about at least twoaxes.
 24. An ultrasound imaging device, comprising: a probe housing; atleast two ultrasound transducer arrays disposed on our near the probehousing; and at least one hinge mechanism configured to couple each ofthe ultrasound transducer arrays to the probe housing, the hingemechanisms configured to allow adjustment of the position or orientationof the ultrasound transducer arrays so as to conform to a physiology ofinterest.
 25. The device of claim 24 further comprising a lockingmechanism configured to lock the hinge mechanisms.
 26. A method ofultrasound imaging, comprising: placing an ultrasound imaging probehaving at least two ultrasound arrays into contact with a patient;allowing each of the ultrasound arrays to individually conform to thephysiology of the patient; locking the ultrasound arrays into aconformed configuration; calibrating the ultrasound imaging probe in theconformed configuration; and after the calibrating step, generatingultrasound images of the patient with the ultrasound imaging probe.